It is known to illuminate sheet material samples to enable inspection for flaws in the surface.
One particular example is for painted surfaces, such as for example automobile bodies, where the paint or the underlying surface is inspected for flaws. Most automobile manufacturers use robotics and an automated painting system to apply various coats of paint to create the paint surface on the automobile bodies that are then used to create the complete automobile. While such systems generally perform satisfactorily, most manufacturers have a quality review of the paint job prior to approving the painted car body for assembly into the completed car.
The quality control can be based on manual visual inspection or automated image processing of images captured by cameras.
A manual inspection process typically involves workers manually moving around each automobile body as it moves along a conveyor and visually scanning the automobile body for a number of different possible flaws.
The workers are generally given only a short time (for example only several minutes) to evaluate the entire automobile body. Generally, there is a paint inspection station that has sufficient room for the workers to walk around each car body. The standard approach is to provide as much direct light as possible to the car bodies during the inspection process, based on the understanding that the more light, the easier it is to visually identify flaws. The emphasis is on lighting the car body.
The inspection workers must watch for as many as several tens of different types of flaws or defects. For example, if there is an underlying flaw such as a raised portion or recessed portion in the car body metal, this will normally be reflected in a raised or recessed portion respectively in the paint job. Also, such things as dust or other particles that may have settled on the car body prior to or during painting will result in a noticeable flaw.
Presently, automobile paint jobs are multi-coat. For example, a first coat or a neutral color rust inhibitor of fairly matte finish (sometimes called an “E” coat), is applied to the metal. A primer coat, usually neutral with a somewhat matte finish or the same color as the ultimate car color, is applied to the first coat. Finally, one or more top coats, for example, a base coat plus a clear coat can be applied over the primer coat.
The first coat is generally inspected for uniformity, flaws and foreign materials. The primer coat is analyzed for flaws, evenness, uniformity, dirt, cavities, runs, and negative or positive depressions in the metal. The top coat creates a highly reflective surface which is inspected for such things as evenness, white spots, striations, swirl marks and other flaws.
If a flaw is identified, the workers attempt to polish it out on the spot, or the car body must be towed from the assembly line to another location for paint repair.
Providing a good lighting solution can help workers in the car factories to detect the defects early and effectively. However, the current approach of bathing the car body in light is not found to be ideal, and workers sometime rely on their hands rather than eyes to detect defects on car body.